1. Field of the Invention
This invention relates to an air passage switching device for switching air passages by moving in the air passages a film member (film door) in which are formed openings for air to pass through, and an air conditioning apparatus in which this air passage switching device is used.
2. Related Art
Air passage switching devices for switching air passages by moving a film door of this kind in related art include for example that disclosed in Japanese Patent Application Laid-Open No. H8-2238. In this related art, the ends of a flexible film door such as a resin film are joined to a driving shaft (first rotating shaft) and a driven shaft (second rotating shaft) rotatably mounted in an air-conditioner case; the ends of the two shafts are coaxially connected to pulleys, and the ends of a wire are wound around these pulleys. A motor is connected to the driving shaft and rotates the driving shaft.
When the driving shaft rotates in the direction in which it takes up the film door, the driving shaft directly takes up the film door and the film door moves. Conversely, when the driving shaft rotates in the direction in which it lets out the film door, this rotation of the driving shaft is transmitted to the driven shaft via the pulleys and the wire, and the driven shaft rotates in the direction in which it takes up the film door and the film door is thus moved and taken up by the driven shaft.
By the film door being moved in forward and reverse directions inside the air conditioner case in this way, air passages such as ventilation air passages leading to a vehicle passenger compartment can be switched freely.
However, in this related art, interference between moving members, such as the pulleys and the wire, and parts such as a ventilation duct around the air conditioner case has been a problem, and the freedom of design of these parts has diminished, resulting in increased manufacturing cost.
Furthermore, because a mechanism connecting two pulleys with a wire is provided as described above to make the driving shaft and the driven shaft cooperate, there has been the problem that the number of parts in the apparatus as a whole is increased, its assembly is complicated, and its cost is increased.
In German Patent No. 3,514,358, an air passage switching device using a film door in which it is possible to dispense with the above-mentioned connecting mechanism (pulleys and wire) is disclosed.
FIG. 29 shows schematically the basic construction of this related art dispensing with the connecting mechanism. As shown in FIG. 29, it has a driving motor 100, a driving shaft 101, a film door 102 and a driven shaft 103, and a driving coil spring 104 is connected to the driven shaft 103.
According to this related art, when the driving shaft 101 is rotated by the driving motor 100 in the direction 1 in which it takes up the film door 102, the driven shaft 103 is rotated by the film door 102 and winds up the coil spring 104. And when the driving shaft 101 is rotated by the driving motor 100 in the opposite direction 2 in which it lets out the film door 102, because the coil spring 104 unwinds under its own spring force, the driven shaft 103 is rotated back in that direction by the spring force of the coil spring 104 and the film door 102 is taken up by the driven shaft 103.
According to this related art, because when the driving shaft 101 is driven by the driving motor 100 to rotate in the direction 1 in which it takes up the film door 102 the coil spring 104 is wound up, the spring force due to winding of the coil spring 104 increases in proportion to the distance moved (stroke) of the film door 102. In other words, the operating force on the film door 102 increases in proportion to the distance moved by the film door 102.
This will now be explained with reference to FIG. 5, in which 1 and 2 respectively correspond to the direction 1 in which the film door 102 is taken up by the driving shaft 101 and the direction 2 in which it is returned to the driven shaft 103 in FIG. 29. When the film door 102 is taken up by the driving shaft 101 (movement direction 1,) the wound up amount of the coil spring 104 increases as the movement distance of the film door 102 increases. Accordingly, the torque T.sub.1 necessary for the winding up of the coil spring 104 increases.
Here, the torque T.sub.0 required to move the film door 102 is always fixed, irrespective of the distance moved by the film door 102, and therefore, when the film door 102 is taken up by the driving shaft 101, the film door take-up torque required of the driving motor 100 increases as the distance moved by the film door 102 increases, as shown with the solid line 1 in FIG. 5.
When on the other hand the film door 102 is returned from the driving shaft 101 to the driven shaft 103 (movement direction 2), the coil spring 104 unwinds under its own spring force and the driven shaft 103 is rotated in the opposite direction by the spring force of the coil spring 104 and the driven shaft 103 takes up the film door 102, and therefore the film door take-up torque required of the driving motor 100 becomes zero, as shown with the solid line 2 in FIG. 5.
However, in this related art, there is no mention of countermeasure for the operating force on the film door 102, which increases with the stroke of the film door 102. Consequently, there may be a risk of a torque shortage of the driving motor 100 during the process of moving the film door 102 in the direction 1 in which the coil spring 104 is wound up and of consequent defective operation of the film door 102.